Outbreak of a novel avian influenza
Here’s a special treat for all BIO230 students; due to a lapse in bonus submissions, I have at least temporarily regained control of the class blog. Alert BIO230 correspondent Heather G has requested an update on H7N9 influenza, a novel influenza isolate that epidemiologists worried, because of its lethality and its potential for further spread.
In late March 2013, the Chinese Centers for Disease Control reported laboratory confirmation of 3 cases of human infection due to an avian influenza, which was determined to be of the H7N9 variety, which had previously never been documented to cause infection in humans. The US Centers for Disease Control and Prevention published a summary of the outbreak this week in the Morbidity and Mortality Weekly Report. As of the end of April 2013, Chinese authorities had confirmed 126 cases of human infection in 8 eastern Chinese provinces, with a fatality rate of 19%. All cases to date appear to be sporadic and of environmental origin, as no obvious human to human contact has been demonstrated outside of 3 family clusters. The origin of the human cases remains under investigation, but is presumed to be due to exposure to live poultry such as chickens or ducks. Of the positive cases for which a complete patient history was available, approximately 75% of the patients has an underlying medical issue which may help to explain their susceptibility to the virus. The US CDC has requested domestic medical laboratories to be on increased surveillance to the disease, particularly with individuals who may have recently returned from this area of China.
Chinese laboratories have already sequenced the genome of this H7N9 isolate, and determined that all of the genes of the virus are of avian origin as opposed to being derived from genetic recombination between avian and mammalian viruses. The viral genome does contain several mutations which increase the ability of this virus to bind to and infect mammalian respiratory epithelial cells, and therefore contribute to the increased virulence of this isolate. Further analysis of this H7N9 variety indicate the presence of resistance genes to the adamantanes, which are a class of important antiviral medications. Consequently, this class of antiviral medications would not be indicated to treat this outbreak.
Chinese authorities are expanding surveillance into potential animal reservoirs with widespread laboratory screening in bird and mammal populations. So far 68,000 bird samples have been screened with 46 positive results. At the same time, 4500 swine samples were examined with no positive results. This suggests that within environmental reservoirs that the virus is being restricted to avian populations. The US government does not allow the importation of live birds, poultry, or eggs from regions with an active highly pathogenic outbreak, and are working to deploy screening procedures to assess whether wild bird populations might be able to import Eurasian influenzas into North American populations.
Editorial notes by the CDC report stress the worrisome nature of this outbreak, primarily because of the speed with which it arose, and because this is the first documented infection of an influenza variety previously believed to be restricted to birds. The CDC recommends that domestic clinical laboratories have plans in place to identify cases here should they arise, and to consider H7N9 infection in patients who have recently returned from areas where the outbreak is continuing. At present, authorities do not feel that travel to China should be restricted, however travelers should practice hand hygiene and safe food practices. Travelers should seek medical treatment for any upper respiratory-associated disease during or after return from travel.